In recent years, in accordance with high performance and high speed operation of smartphones, tablet PCs and the like, for semiconductor packages used therefor, further downsizing, high capacity, high speed operation and thinning have been required. Thus, in wafers used in semiconductor packages, further miniaturization of interconnects proceeds, and additionally, chips tend to become further thinner on assembling packages.
In such trends, particularly in the field of DRAM and NAND type flash memories in recent years, the problem of the occurrence of malfunctions due to a trace amount of heavy metal ions such as copper ions has become obvious.
It has been long known that when heavy metal ions come in contact with a silicon crystal, the ions diffuse in the crystal and reach the circuit surface, and as a result, a malfunction occurs. Therefore, it is common to conduct gettering treatment on a silicon wafer for capturing heavy metal ions such that the heavy metal ions attached to the silicon wafer do not diffuse to the circuit surface.
As the gettering treatment, for example, a method of providing a gettering layer within the wafer (intrinsic gettering, referred to as “IG” hereinbelow) and a method of providing a gettering layer on the back side of a wafer (extrinsic gettering, referred to as “EG” hereinbelow) are predominantly used. However, thickness of the gettering layer that can be formed inside is becoming thinner because of thinning of chips in recent years, and it is becoming hard to say that its effect is sufficient. Additionally, in EG, fine cracks are formed on the back side of a wafer, and therefore, flexural strength of the chip decreases. Thus, particularly in ultrathin wafers of which handling is difficult, the problem of excessive gettering treatment being difficult to conduct has occurred. Under such circumstances, imparting a gettering function to a die bonding film used for adhesion between a chip and a substrate or between a chip and a chip has been contemplated in recent years (for example, see Patent Literatures 1 and 2 below).
However, in the case of determining if a gettering function is imparted by such materials, it is necessary to make an evaluation after a package is actually prepared using a substrate on which a wiring layer is formed or a wafer on which a circuit is formed. In this case, there is a problem that a large amount of cost, a long period of time, apparatuses and the like may become required.
Under such situations, a new evaluation method has been contemplated for determining if a material for semiconductors has a gettering ability or not. For example, in the Patent Literature 3 below, there is represented a method in which one side of a silicon wafer is contaminated with heavy metal, the heavy metal is allowed to diffuse by heating, a film, which is an object to be evaluated, is applied to the contaminated one side, and after thermal treatment under pseudo reflow conditions, the amount of heavy metal ions on the other side of the silicon wafer (no contaminated side) is measured, Furthermore, in the Patent Literature 4 below, there is represented a method in which a film, which is an object to be evaluated, is applied to one side of a silicon wafer, the film surface is contaminated with heavy metal, and then, thermal treatment is conducted under pseudo reflow conditions, and the amount of heavy metal ions on the other side of the silicon wafer (the side to which no film is applied) is measured.